arrays1 © 2014 goodrich, tamassia, goldwasser presentation for use with the textbook data...
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Arrays 1
Arrays
© 2014 Goodrich, Tamassia, Goldwasser
Presentation for use with the textbook Data Structures and Algorithms in Java, 6th edition, by M. T. Goodrich, R. Tamassia, and M. H. Goldwasser, Wiley, 2014
Arrays 2
Array Definition An array is a sequenced
collection of variables all of the same type. Each variable, or cell, in an array has an index, which uniquely refers to the value stored in that cell. The cells of an array, A, are numbered 0, 1, 2, and so on.
Each value stored in an array is often called an element of that array.
A0 1 2 ni
© 2014 Goodrich, Tamassia, Goldwasser
Arrays 3
Array Length and Capacity Since the length of an array determines the
maximum number of things that can be stored in the array, we will sometimes refer to the length of an array as its capacity.
In Java, the length of an array named a can be accessed using the syntax a.length. Thus, the cells of an array, a, are numbered 0, 1, 2, and so on, up through a.length−1, and the cell with index k can be accessed with syntax a[k].
a0 1 2 nk
© 2014 Goodrich, Tamassia, Goldwasser
Declaring Arrays (first way) The first way to create an array is to use an
assignment to a literal form when initially declaring the array, using a syntax as:
The elementType can be any Java base type or class name, and arrayName can be any valid Java identifier. The initial values must be of the same type as the array.
© 2014 Goodrich, Tamassia, Goldwasser Arrays 4
Declaring Arrays (second way) The second way to create an array is to
use the new operator. However, because an array is not an instance
of a class, we do not use a typical constructor. Instead we use the syntax:
new elementType[length] length is a positive integer denoting the
length of the new array. The new operator returns a reference to
the new array, and typically this would be assigned to an array variable.
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Arrays of Characters or Object References An array can store primitive elements,
such as characters.
An array can also store references to objects.
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Java Example: Game Entries A game entry stores the name of a player and her best score so far in a
game
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Java Example: Scoreboard
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Keep track of players and their best scores in an array, board
The elements of board are objects of class GameEntry Array board is sorted by score
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Adding an Entry To add an entry e into array board at index
i, we need to make room for it by shifting forward the n - i entries board[i], …, board[n – 1]board
0 1 2 ni
board0 1 2 ni
0 1 2 nei
© 2014 Goodrich, Tamassia, Goldwasser
board
Java Example
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Arrays 11
Removing an Entry To remove the entry e at index i, we need to fill
the hole left by e by shifting backward the n - i - 1 elements board[i + 1], …, board[n – 1]
0 1 2 ni
0 1 2 nei
0 1 2 ni
© 2014 Goodrich, Tamassia, Goldwasser
board
board
board
Java Example
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